1. Field of the Invention
This invention relates to a manifold reactor for an internal combustion engine, and more particularly to improvements in an inner core and supporting members therefor so as to minimize the thermal stress created therein.
2. Description of the Prior Art
A manifold reactor is well known in an exhaust system for the purposes of converting or purifying exhaust gases from an internal combustion engine and includes an inner core and an outer core. It has been a common practice that the inner core is secured by welding to the outer core through means of supporting members. With such an arrangement, the interior of the inner core serves as a re-combustion chamber.
For achieving improved conversion, exhaust gases should be maintained at a high temperature and the size of the recombustion chamber should be increased so as to extend the dwelling time of the streams of exhaust gases through the re-combustion chamber. This, however, poses another problem in that the inner core, having considerable weight, has to be supported by inner-core supporting members, thereby limiting an increase in size of the re-combustion chamber from the viewpoint of strength of the construction.
On the other hand, the loads borne by the individual innercore supports may possibly be reduced by increasing the number of the supports. However, this only meets with partial success, since thermal expansion of the inner core, which is restricted by such an increased number of inner core supports, creates excessive thermal stresses in the supports. This, in turn, causes the failure or cracking in weld joints interconnecting the inner core and the inner-core supports or the outer core and the inner-core supports. Such failure and cracking then cause a reduction in the output of an engine or creates unwanted noises, and may even cause peeling and scattering of insulating materials within the manifold reactor, thus eventually neutralizing the functions of the manifold reactor completely.
More particularly, the inner-core support usually assumes a band form having a given length, its central portion being welded to the inner core and its end or leg portions being suitably bent and welded to the inner surface of the peripheral wall of the outer core according to a fillet-welding or a plugwelding technique. The inner-core supports are arranged in pairs in symmetric relation with respect to the inner core, as viewed in its cross section. In this respect, the inner-core support is placed crosswise of the inner core.
The strength of a fillet-welded joint interconnecting the inner-core support and the outer periphery of the inner core is not uniform, because of the irregular shapes of the opposite ends of the weld beads, so that stress concentration tends to take place at such ends. In addition, the ends of a weld bead and their heat-affected zones are likely to cause cracking due to thermal stresses which are created at the time of welding or due to a repeated cycle of heating and cooling of the manifold reactor, as experienced in service. As is well known, cracking thus caused will be the source of stress concentration. Cracking often takes place in the craters at the ends of a weld bead.
The weld beads interconnecting the inner core and the innercore support, according the prior art, therefore, cause defects such as cracking, as do the thermal stresses by being exposed to high temperature exhaust gases in service, with the result of separation of the inner-core support from the inner core.
It is accordingly desired to avoid the results of weld defects and the accompanying stress concentration due to thermal stresses caused by thermal expansion of the inner core and due to the repeated cyle of heating and cooling of the manifold reactor in service.